1. Field of the Invention
The present invention relates to a method of forming a contact hole and a method of manufacturing a semiconductor device.
2. Related Background Art
In recent years, packing density of an LSI (Large Scale IC) increases rapidly and the cost in a lithography process sharply rises. Concretely, as the packing density increases (as an LSI becomes finer), the wavelength of exposure equipment is shortened or the numerical aperture of the exposure equipment becomes higher, so that the cost of exposure equipment increases.
A problem arises such that the techniques of shortening the wavelength and increasing the numerical aperture of exposure equipment cannot catch up with the speed of increase in packing density.
More specifically, in the lithography technique, it is particularly difficult to form a finer contact hole. It is very difficult to increase contrast to the optical image for a contact hole only by shortening the wavelength of exposure equipment or increasing the numerical aperture (achieving higher NA).
There is a technology such that a pattern of a linear space is transferred to a wafer, another pattern of a linear space orthogonal to the pattern of the linear space is transferred to the wafer, and a contact hole pattern is formed at the intersecting point of the linear spaces. To increase resolution of a contact hole by using the technology, it is preferable to transfer a pattern having repetition of a line and a linear space (lines and linear spaces) as each of the patterns. Specifically, by using a mask having a pattern having lines and linear spaces and a mask having a pattern having lines and linear spaces which are orthogonal to the pattern of lines and linear spaces (total two photo masks are used), contact hole patterns regularly arranged at lattice points in square are formed at the intersecting points of the linear spaces.
On the other hand, there is also a method of forming cyclic patterns and selectively leaving only necessary patterns of the cyclic patterns.
By combining the above two techniques, as described in JP-A 10-232496, contact hole patterns having a desired layout can be formed.
This method, however, requires three photo masks. From the viewpoint of cost, it is difficult to employ the method.